Problem: Simplify the following expression: $x = \dfrac{1}{10p} - \dfrac{3}{7p}$
In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $10p$ and $7p$ $\lcm(10p, 7p) = 70p$ $ x = \dfrac{7}{7} \cdot \dfrac{1}{10p} - \dfrac{10}{10} \cdot \dfrac{3}{7p} $ $x = \dfrac{7}{70p} - \dfrac{30}{70p}$ $x = \dfrac{7 -30}{70p}$ $x = \dfrac{-23}{70p}$